The applicant proposed a non-contact type rotary sensor which utilizes a hall element as shown in FIG. 6, in Japanese patent application No. H11-255409. This rotary sensor 10 comprises a first stator 11 having two magnet-facing sides 11a, 11b, a second stator 12 having one magnet-facing side 12a, a hall element 13 provided between the first and second stators, moving magnets 14, 15, and a rotor 16 to fix these moving magnets.
The three magnet facing sides 11a, 11b, 12a are arranged on nearly the same arc and, together, practically form a circle. On the other hand, the moving magnets 14, 15 are plate-shaped magnets that are curved into arc shapes at their magnet-facing sides, wherein the arc shapes have the same center of curvature. The magnets 14, 15 have poles in the plate thickness direction, and are arranged along the arc so that the poles of the moving magnets that are located next to each other are opposite to each other. The rotor 16 rotates along the arc.
In this example, when the moving magnets 14, 15 move along the arc, the magnetic flux passing through the hall element 13 changes. Therefore, by detecting the changes, the rotating angle of the rotor can be detected. Here, because the length of the two magnet-facing sides 11a, 11b of the first stator 11 can be set appropriately, the angle range of usage can be obtained as desired, and the resolution can be improved in this range.
FIG. 7 is a sectional view of the abovementioned rotary sensor in the assembled state, and FIG. 8 is a sectional view along line VIII—VIII in FIG. 7. As shown in FIG. 7, the first stator 11 and the second stator 12 are disposed in a case 17, and the hall element 13 is inserted between the stators.
The space inside the case 17 in which these are fitted is covered by a cover 18. A center pin 18a is mounted to the cover 18, and is fitted to a bearing hole 16a of the rotor 16 penetrating the first stator 11.
In ordinary cases, the rotor 16 receives offset force by the attracting force of the moving magnets 14, 15 to make the moving magnets 14, 15 get closer to the first and the second stators. However, the operation accuracy is maintained and the rotor 16 can rotate smoothly, because the center pin 18a is fitted to the bearing hole 16a of the rotor 16, and the slight clearance between the center pin and the bearing hole is offset. Further, in case the rotor 16 is shifted to the direction of the length of the center pin 18a, it is attracted to a certain position by the attracting force between the moving magnets 14, 15 and the first and the second stators 11, 12. Based on the description above, the rotary sensor of this type is impervious to being swung by vibration, and as a result, has an advantage of not producing output fluctuations.
A hole 16b is formed at the opposite side of the rotor 16 to which a rotating shaft 19 as a counterpart is fitted. As shown in FIG. 8, a cut portion 19a, which is called a D-cut from its sectional shape, is formed at the top end of the rotating shaft 19. In addition, the hole 16b has the same shape as the D-cut portion 19a of the rotating shaft. Therefore, when the D-cut portion 19a is fitted to the hole 16b, the rotation of one can be transferred to the other.
When the abovementioned rotating shaft 19 and the hole 16b of the rotor are fitted together, it is ideal that the axes of both of them are perfectly aligned. However, it is actually normal that there is some misalignment because of the variation of accuracy at the time of production.
Therefore, the rotor 16 is inclined due to the misalignment, and the distance T′ between moving magnets 14, 15 and the first and the second stators 11, 12 which is shown in FIG. 7 fluctuates, and the detecting accuracy of the non-contact type rotary sensor 10 is greatly affected.
The present invention was devised in the light of the above-mentioned facts, and it is an object to provide a rotary sensor which can detect accurate angles even if there is some misalignment between the center of the rotor and the center of the rotating shaft.